Vehicles, in particular commercial vehicles, are increasingly being equipped with sensor systems by which the vehicle surroundings can be sensed. Such sensor systems can be used to operate assistance systems and safety systems. The underlying principle of these systems is that a certain value is predefined for a variable that is relevant for the vehicle (setpoint value). In assistance and safety systems, these variables relate, in particular, to the state of movement of the vehicle, for example to the speed of the vehicle. The current value of this variable is measured (actual value) using a suitable measuring system. The current actual value is compared with the setpoint value using a control unit. If the actual value differs from the setpoint value, the control unit generates a control signal with which built-in units, for example a brake system or an engine controller, which relate to the state of movement of the vehicle, can be actuated. The actuation of these built-in units causes the actual value to approach the setpoint value until the two values correspond to one another. In this case, actuation of the brake system or of the engine controller would therefore cause the speed to be changed until the vehicle has reached the predefined speed. For example, a cruise controller is based on this principle.
A further example of such an assistance function that is widely used is adaptive cruise control (ACC). The distance from a vehicle travelling ahead is determined using a distance sensor and is adjusted automatically by means of a cruise control system. Depending on the embodiment, the distance to be maintained from the vehicle travelling ahead can be input manually or permanently predefined at the factory. In addition, the distance to be maintained can be adapted automatically to the current speed of the vehicle. The extent of the distance from the vehicle travelling ahead is an example of a traffic-situation-related criterion or of a traffic-related threshold value. The adjustment of the distance is brought about, for example, by increasing or reducing the torque demand that is made of the engine or additional activation of the brakes. The maximum decelerations triggered by the ACC are, according to the ISO standard, typically significantly below those of full braking operations since the ACC is only a comfort system. The reliability of detection of the distance sensors used today is generally not sufficient to trigger a full braking operation based thereon. For this reason, in these systems, the deceleration is artificially limited in order to avoid placing the driver of the vehicle in question or the traffic following behind in danger in the case of incorrect triggering. In addition, the driver can override such a system at any time by activating, for example, the accelerator pedal or brake pedal. In addition, it lies within the freedom of decision of the driver whether the driver will activate the ACC at all. If, in the case of an active ACC, avoidance of an accident requires a greater deceleration than the maximum deceleration made available by the ACC, it is the driver's responsibility to apply such deceleration. Consequently, ACC systems are only suitable to a very limited degree for avoiding collisions or for reducing the severity of collisions.
EP 1 559 607 A1 describes a method that, regardless of an active ACC, in the event of an imminent collision, requests the driver by means of a warning to carry out an accident-avoiding action, such as for example an emergency braking operation. Furthermore, there are also approaches for avoiding accidents or for reducing the consequences of accidents that are generally referred to as collision mitigation systems (CMS).
Such systems generally use the same distance sensors that are used in ACC systems. The known limitations of ACC systems are, for example, unreliable detection of vehicles that are already stationary or possible incorrect detection, which can be triggered, for example, by multiple reflections at structures along the boundaries of the road (crash barriers, signs, bridges). Precise measurement of the width of the objects and of the lateral offset in relation to the direction of movement of the driver's own vehicle is likewise impossible, or possible only to a very unsatisfactory degree, with the vast majority of the distance sensors available on the market. For this reason, assessment of a possible avoidance manoeuvre, which is customary in collision-avoidance systems, either cannot be carried out at all or can only be carried out very imprecisely. In addition, there is no redundant confirmation of a relevant object, which is necessary for a safety-related system, for example for triggering an autonomous emergency braking operation.
The risk is that, in the case of repeatedly occurring incorrect warnings, the driver tends to ignore the warnings, which can have serious consequences and which makes the systems useless when a hazardous situation actually occurs. In addition, in the case of emergency braking operations that are triggered incorrectly there is also the risk of tail-end collisions with vehicles following behind, which is also unacceptable in a situation that is not critical in terms of collisions.
As a result, nowadays, either significant limitations have to be placed on the performance of such collision-warning/consequence-reducing systems or an increased number of incorrect warnings/incorrect reactions have to be tolerated.
A further sensor-assisted and widespread assistance function is the lane departure warning (LDW) system. LDW systems are video-supported systems for sensing the course of a roadway (peripheral markings or lane markings) and for determining whether the vehicle will unintentionally leave the prescribed lane (i.e., without the direction indicator being set by the driver). Such systems are useful, in particular, if the driver is distracted by other activities (for example operation of the radio) or generally has problems in correctly following the course of the lane due to a lack of concentration. However, such systems do not serve to avoid collisions with vehicles travelling ahead but rather to avoid collisions that are due to the fact that the driver has unintentionally departed from the driver's own lane.